The present invention relates to an advantageous and highly effective method of preserving wood and construction materials made of wood, to preserving compositions used for said method, and to wood and materials made of wood preserved by means of such compositions, and more particularly to highly advantageous preserving compositions containing specific fungicides or mixtures of specific fungicides, and, if desired, also specific insecticides, dissolved in a difficultly volatile organic-chemical solvent or solvent mixtures of a specific flash point.
It is known to use N,N-dimethyl-N'-phenyl-N'-(fluoro dichloro methylthio) sulfamide as a fungicidal agent for preserving wood. See the journal "Holz als Roh- und Werkstoff," Vol. 25 (1977), pages 233 to 237. However, when using said, N,N-dimethyl-N'-phenyl-N'-(fluoro dichloro methylthio) sulfamide, there are encountered, among others, the disadvantages that, on the one hand, this compound dissolves difficultly or only slightly in the conventional formulation in aliphatic and aromatic organic solvents, whereas, in comparison with some other active compounds, higher concentrations of this compound are required in order to achieve a satisfactory fungicidal effect on the treated wood. On the other hand, another disadvantage of the above mentioned sulfamide is that this compound, after it has been applied to the wood, can partly crystallize on the surface of the wood in the form of fine, white crystals. Such blooming of the fungicidal agent N,N-dimethyl-N'-phenyl-N'-(fluoro dichloro methylthio) sulfamide ought to be prevented because it causes a loss in effectiveness and renders the wood surface unattractive.
Furthermore, the use of N,N-dimethyl-N'-(p-tolyl)-N'-(fluoro dichloro methylthio) sulfamide as a fungicidal agent and especially as a plant protective agent, is known. N,N-Dimethyl-N'-(p-tolyl)-N'-(fluoro dichloro methylthio) sulfamide has the advantage over N,N-dimethyl-N'-phenyl-N'-(fluoro dichloro methylthio) sulfamide that it is somewhat better soluble in certain organic solvents than the latter compound. However, when using N,N-dimethyl-N'-(p-tolyl)-N'-(fluoro dichloro methylthio) sulfamide dissolved in conventional solvents as a wood preserving agent, there can also occur formation of crystals or blooming of N,N-dimethyl-N'-(p-tolyl)-N'-(fluoro dichloro methylthio) sulfamide on the surface of the wood, especially at concentrations of the active agent exceeding 1%. Such formation of crystals and blooming on the wood surface renders the appearance of the wood quite unattractive and, furthermore, causes some loss of fungicidal agent within the wood.
If in a wood preserving composition one employs as the fungicidal agent either N,N-dimethyl-N'-phenyl-N'-(fluoro dichloro methylthio) sulfamide or N,N-dimethyl-N'-(p-tolyl)-N'-(fluoro dichloro methylthio) sulfamide and a binding agent which is soluble in the solvent used, for instance, an alkyd resin or linseed oil, upon applying such a wood preserving coating composition, and more particularly, as a wood preserving glazing or impregnating undercoating composition, there frequently is observed formation of a whitish incrustation of N,N-dimethyl-N'-phenyl-N'-(fluoro dichloro methylthio) sulfamide or N,N-dimethyl-N'-(p-tolyl)-N'-(fluoro dichloro methylthio) sulfamide on the surface of the coating or a milky turbidity in the coating itself. Sometimes this phenomenon may be observed only after several weeks or even months. It results, on the one hand, in a decrease of the effectiveness of the wood preserving composition and, more particularly, in a decrease in the effectiveness of the fungicidal agent contained therein, and, on the other hand, in an impairment of the surface of the coating or of the wood treated therewith. Due to this, the decorative effect of the treated wood surface is considerably diminished. The resulting bloomings, turbidities, and the like, can be removed by washing, but only with great difficulty. When attempting to rub them off, they are frequently spread over the whole surface of the treated wood (most probably due to the formation of crystal nuclei). Thus, any attempt to rub off the crystalline deposits can frequently even cause an intensification of the "blooming effect."
This "blooming effect" is especially encountered when applying preparations of N,N-dimethyl-N'-phenyl-N'-(fluoro dichloro methylthio) sulfamide and/or N,N-dimethyl-N'-(p-tolyl)-N'-(fluoro dichloro methylthio) sulfamide having a concentration exceeding 1% (calculated based on the wood preservation composition). These disadvantageous effects, however, can be observed also at lower concentrations, i.e., at concentrations below 1% of N,N-dimethyl-N'-phenyl-N'-(fluoro dichloro methylthio) sulfamide and/or N,N-dimethyl-N'-(p-tolyl)-N'-(fluoro dichloro methylthio) sulfamide, depending upon the composition of the wood preservative, the solvents employed, the temperature at which the preparations are applied and used, the kind of wood to be treated, and the like.
Many fungicidal agents used in preparing wood preserving compositions cannot be stored for a prolonged period of time or partly lose their effectiveness when used in combination with synthetic resins or certain solvents, or during drying of the coatings applied to the wood or materials made of wood. It would be advantageous to be able to use wood preserving compositions which contain as the fungicidal agents, two of the most effective fungicides, namely, N,N-dimethyl-N'-phenyl-N'-(fluoro dichloro methylthio) sulfamide and/or N,N-dimethyl-N'-(-tolyl)-N'-(fluoro dichloro methylthio) sulfamide. These fungicides do not exhibit the aforesaid disadvantages, such as instability on storage and are, according to available test data, essentially unobjectionable from a hygienic standpoint.